Groundwater Contamination (1984) / Chapter Skim
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10. Hydrogeochemical Studies at a Landfill in Delaware
10. Hydrogeochemical Studies at a Landfill in Delaware
Pages 127-138
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From page 127... ...
APGAR Department of Natural Resources and Environmental Control, Delaware AB STRACT Plumes of leachate have migrated downgradient from the Army Creek landfill in Delaware, a site used for disposal of industrial and municipal refuse during the 1960s. A series of contaminant-recovery wells was installed in the early 1970s between the landfill and downgradient water-supply wells to intercept and remove contaminated water.
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From page 128... ...
The purposes of this chapter are to review groundwater contamination at a landfill, examine and interpret hydrologic and chemical data available from 1973 to 1981, describe the hydrogeologic processes and chemical reactions that have affected the groundwater chemistry, and discuss the results in terms of long-range planning and management of contaminated aquifers. The landfill studied is the Army Creek landfill, previously known as the Llangollen landfill, in New Castle County, Delaware.
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From page 129... ...
3 ~ D ~ ~ . Three major well fields the county's contaminant recovery system and those operated by the Amoco Chemical Corporation and the Artesian Water Company account for all pumping in the area.
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From page 130... ...
Although for the past 5 yr the position of the 50 m0L isochlor has changed little, the location of the plume and the relative pumpage of the Artesian Water Company and the contaminant-recovery well are in delicate balance. The distribution of C1- in the major leachate plume south of the landfill showed the most striking change before 1977 (Figure 10.61.
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From page 131... ...
The latter remedial measures were estimated in 1978 at $4 million to $6 million in capital and $1 million in annual maintenance costs (Anonymous, 19781. GEOCHEMICAL ASPECTS Sampling Techniques Water samples were collected on the landfill with a metal bailer from 1973 to 1976 and by a peristaltic pump from 1976 to 1981.
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From page 132... ...
Large amounts of O2 are removed from the native groundwater by the oxidation of organic matter and dissolution of metals. In fact, more O2 than is available in native groundwater is needed to account for the amount of iron precipitated and total inorganic carbon (CO32-, HCO3-, H2CO3)
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From page 133... ...
The water chemistry in this zone results largely from mixing of leachate with native groundwater, with only minor changes as a result of chemical reactions. The values for DS in this zone ranged from 50 to 160 mg/L in 1981, which is about 30 percent lower than those measured in 1977.
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From page 134... ...
However, CH4 has continued to move downgradient and is present in water containing as much as 1.7 mg/L of O2 TABLE 10.1 Dissolved Organic Carbon and Volatile Organic Compounds (VOC) in Groundwater at Army Creek Landfill VOC (~g/L)
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From page 135... ...
The controlling reactions and processes that alter the chemical composition of leachate as it moves along a groundwater-flow path were simulated by a chemical mass-balance model. The first calculation in the model is to evaluate the role of mixing of the contaminated water with native groundwater.
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From page 136... ...
Because the confining layer is thin close to the landfill and the partial pressures of CO2 and CH4 are high, outgassing is possible in this part of the aquifer. Iron precipitates as either siderite or amorphous iron oxide based on thermodynamic saturation data calculated by the chemical equilibria computer program WATEQF (Plummer et al., 19761.
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From page 137... ...
operation of the recovery-well system that removes contaminated water and reverses the local flow, (2) dilution of leachate with native groundwater, (3)
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From page 138... ...
Thus, the extent of leachate movement within the aquifer is determined by factors that influence groundwater velocity, which include the rates of pumping recovery and supply wells. The recovery-well system has effectively retarded the movement of contaminants from Army Creek landfill to the Potomac aquifer.
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